Films employing metal nanowires, such as, for example, silver nanowires (AgNWs), are replacing films based on indium tin oxide (ITO) in some end-use applications, because of their improved transparency, durability, and flexibility.
For many applications, such as, for example, capacitive touch screen devices, films are patterned to provide regions of differing conductivities. The presence of a finger may thereby be detected by control circuitry attached to the patterned film. For films based on ITO, non-conductive regions can be formed by chemically etching and removing portions of the film. See, for example, Ghezzo, U.S. Pat. No. 3,979,240; Ponjee et al., U.S. Pat. No. 4,093,504; and Miyagaki et al., U.S. Pat. No. 5,094,978, each of which is hereby incorporated by reference in its entirety. This approach has also been applied to films based on AgNWs. See, for example, Allemand et al, U.S. patent application publication 2008/0143906 and Cambrios Technologies Corporation, PCT publication WO2008/046058.
In devices where the patterned film is positioned between an illuminated screen and the user, it is desirable that differences in optical properties between the patterned and unpatterned regions of the patterned film not be discernable by the user. One possible approach to address this problem is to control the patterning conditions so that the difference between the electrical conductivities of the patterned and unpatterned regions is sufficiently high to meet the electrical requirements of the device, while still maintaining minimally discernable differences between the optical properties of the patterned and unpatterned regions. See, for example, Allemand et al., U.S. Pat. No. 8,018,568, which is hereby incorporated by reference in its entirety.